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unixronin: Galen the technomage, from Babylon 5: Crusade (Default)
Unixronin

December 2012

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May 31st, 2010

unixronin: Closed double loop of rotating gears (Gearhead)
Monday, May 31st, 2010 02:10 pm

I just repaired the broken shifter lock button on our Volvo.  The button was badly cracked when we bought the car (a used Volvo XC70 with 98,000 miles on it, for $7000), and broke into three pieces during the first winter we had the car.  I pulled the pieces out, tried various different adhesives without success, and eventually welded the parts back together and reinstalled it. That lasted until last summer or fall, when it broke again along one of the original cracks.  I took the pieces out again, put them on my workbench intending to try another repair, and there they got buried.

Recently, having come up with a plan I thought would work, I dug them out again and had another go.  Yesterday, I broke off all the old weld filler plastic, re-welded the break and the other old crack from both sides to hold it together while I worked on it, sanded all the affected outer surfaces level and slightly rough, then heat-molded a sheet of textured black 3/16" ABS onto it to fit the compound curvature of the front face perfectly.  I then mixed up a batch of two-part epoxy, bedded the button into the new ABS face and epoxied it there, cut a piece of glass mat to fit inside it, and epoxied that into place inside the button to make an internal fiberglass reinforcing layer.  Then, after all of the epoxy cured, I trimmed and sanded the ABS faceplate to the edges of the button and buffed all the exposed edges.

I just went out and installed the repaired lock button (now easily three times its original mass) back into the shifter.  (The dealership, by the way, won't even attempt to replace the button; they'll replace the entire shifter.)  With the dubious benefit of unwanted practice, it only took me about ten minutes to get it in this time, using only a pair of needle-nose pliers and (believe it or not) a dental pick.  It's working perfectly, and looks as though it's always been there.

Functionality restored, cosmetics restored, roughly $400 dealer parts-and-labor bill saved.

WIN.

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unixronin: A mon made from four torii gates (Wisdom/Zen)
Monday, May 31st, 2010 06:48 pm

I have devised a new game for Icehouse pieces, based loosely upon an (unfortunately, overly complex and unworkable) idea that the Dread Pirate Bignum came up with this morning.  The working title of the new game is Rock, Paper, Pyramid (but see the caveat below).

The game works like this:

  1. Rock, Paper, Pyramid is played on a square, hexagonal or octagonal board as available or necessary, allowing for up to eight players.  One full stack of pieces is required per player.  The size of the board is to be such that each player has a row of five adjacent squares along their facing edge which are not shared with any other player.  For example, two players can play on a 5x5 square board, but three players would require at minimum either a hexagon of side 5, or a square of at least side 7.

    (Well, OK, those aren't the only possibilities.  If you want to try to construct a board with pentagonal, heptagonal or nonagonal symmetry, for example ... hey, knock yourself out.  A triangular board for three players would be possible, but would probably be unplayably crowded unless significantly larger than the minimum possible side 7.)

  2. Each player begins play with a stack of pieces along their edge, one nest on each of the five squares.  Each turn, each player may move one piece one square in any direction.  The opening moves must un-nest pieces in top-down order; a piece may not be moved from the bottom of a full or partial nest.  Up to one friendly piece of each size may share any square, but friendly pieces, once un-nested, may never re-nest.

  3. When hostile pieces meet, pieces of the same size block each other.  A S may not move onto a square already occupied by a hostile S, and so on.  Hostile pieces of differing sizes that enter the same square must always either capture or be captured.  L captures M, M captures S, S captures L.  Any piece that moves onto a square containing a hostile piece that could capture it is automatically captured by it at the end of that move.  This does not consume the other player's turn.

  4. Captured pieces remain on the board until the beginning of the next turn of the player whose move initiated the capture.  During this time, the entire stack may be recaptured by another player.  At the beginning of the next turn of the original initiating player, the entire stack, except for the topmost piece, is removed from the board and placed in the capture pile of the player who owns the topmost piece

  5. Special cases:  A partial nest in its starting square that has not yet been fully unstacked can be captured, provided no piece that would block the capturing piece is present on the square.  In practical terms, this means that a L piece can capture a M and S that are still nested.  In this case, the S piece on the bottom of the nest is captured along with the M, and does not automatically capture the attacking L piece.  A full nest still untouched on its starting square cannot be captured, because it automatically blocks all possible attacking pieces.

  6. Victory conditions:  The game can end in one of three ways — Last Man Standing (all players but one have been eliminated); Mexican Standoff (no surviving player can make any non-trivial move that does not result in automatic capture); or stalemate (all players agree that a stalemate has been reached).

  7. Scoring:  In the event of a Last Man Standing victory, the surviving player is of course the winner, and the other players are ranked in reverse order of elimination.  In the event of a Mexican Standoff or a stalemate, victory is determined by counting up the total number of pieces, including the player's own, in each player's capture pile.  Any ties in this count are resolved by a recount of only captured pieces owned by the tied players.  If any players are still tied after recounting ... well, it's a tie.  :)

So far, there's just one problem that hasn't yet been resolved:  [livejournal.com profile] freetrav has pointed out to me that there is already a game called RockPaperPyramid on the Icehouse Games wiki.  So, I need to find a non-conflicting name if I want to post it on Icehouse Games (as suggested by [livejournal.com profile] freetrav).  Rock, Pyramid, Scissors is a possibility, but it doesn't flow as nicely as the one-two-three rhythm of Rock, Paper, Pyramid and I don't really like it.  Suggestions are welcome.

It should be noted that this game has not yet been more than minimally play-tested.

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unixronin: Galen the technomage, from Babylon 5: Crusade (Duty/Loyalty)
Monday, May 31st, 2010 07:09 pm

Terse, but good, and direct to the point:

unixronin: Rodin's Thinker (Thinker)
Monday, May 31st, 2010 10:12 pm

I've made my opinion of the Drake equation clear several times in the past.  Instead of revisiting that, I want to look at SETI from another angle.

Consider if you will what we can "look at" with SETI.  We have been conducting a SETI program for — let's call it an even fifty years.  So, if we handwave for the moment the question of whether we've been looking in the right places or using the right means, and just assume that if a signal existed we would have picked it up (a generous assumption), let's say we have examined a sphere of fifty light years radius for intelligent life.  Let's be even more generous and say that our ability to detect such signals has been constant throughout the lifetime of the SETI project.  (It has not; it's pretty fair to say that it has increased continuously throughout the life of the project.)

In actual fact, it's a little better than that.  You see, if a signal had been sent from fifty-one years away, anywhere from one year to fifty-one years before SETI began, we would (under the generous parameters above) have received it.  Likewise if a signal were sent from 60LY anywhere from ten to sixty years before the beginning of SETI.  In a sense, we can say that we have studied a fifty-year/50LY thick surface layer of a "light cone" stretching back into the galaxy's past and spreading out as it goes.  Any signal sent more than fifty years inside that cone, we missed.  Any signal sent outside it, we haven't received yet.  Any signal sent more than, to be generous again, a hundred years or 100LY outside that cone will probably not be received during the lifetime of anyone now working on SETI (even if only to the extent of running SETI@Home).

OK?

Now.  The galaxy is a hundred thousand light years across.  At any given instant in the past, the intersection of that "light cone" with the galaxy that we have so far examined is fifty light years wide.  That's one two-thousandth of the diameter of the galaxy.  Looks about as thick as a pencil line, doesn't it?  And if we assume that we're "not special", then the further back into the past that light cone propagates, the less likely it is to intersect a technological civilization.

So let's forget about the deep past for now.  Let's instead imagine, for the moment, that the galaxy is seeded with a thousand civilizations comparable and contemporary to our own.  (If they're more than about a hundred years behind us, they can neither send any signals we can detect, nor could they detect any of ours.  If they're more than about a hundred years ahead of us ... who knows what they use for communication.  For all we know, they use phase-modulated artificial gravity waves or quantum-entanglement ansibles.)  Each of them, like ours; is surrounded by an expanding 100LY-radius bubble of radio emissions bearing the signature of intelligent generation.

Pretend, for the moment, that the galaxy has zero thickness.  (It doesn't.  It's about sixteen thousand light-years thick in its central bulge, and about five thousand out here in our region.  But we'll ignore that for now.)  That makes the plane area of the galaxy roughly 7.85 billion square light years (pi times the square of fifty thousand light years).  Let's assume that, on average, civilizations are more or less evenly scattered¹, and divide that area into a thousand roughly equal domains.  Then each of these domains is 7.85 million square light years, from which we can work backwards to find that each of those domains — including our own — has a radius of ... oh dear.  About 707 light years.  Which puts our hypothetical thousand Earthlike civilizations about fourteen hundred light-years apart.  Uh-oh.  The odds are we're not going to hear anything from any of them for a LONG time.

So let's improve the odds.  Let's say there's ten thousand civilizations.  Now those domains are about 785,000 square light years, and their radius is therefore ... um. A hair under five hundred light years.  They still average a thousand light years apart.  That doesn't help us much, does it?

OK, what if there's fifty thousand civilizations?  Well, that about halves the separation.  Domains are now about 225LY radius, making them about 450LY apart ... no.  Still doesn't help us.  To have roughly a 50/50 chance of a detection in the next fifty years, we probably need them to be no more than about 150LY apart on average.  (We'll ignore developmental-stage offsets, because lacking any information to the contrary or any reason to believe that we are somehow "special", the most reasonable guess we can make is that the number of civilizations N years ahead of us is roughly comparable to the number of civilizations N years behind us, for any arbitrarily chosen value of N.  So, without even worrying about distribution, we'll assume they roughly cancel each other out.  Remember, we're working with averages here.)  That means a domain radius of about 75LY.

So, how many civilizations do we need to get the domain radius down to about 75LY?

Turns out we need about half a million.  And that, remember, is not to have a detection now, it's to have a roughly fifty-fifty chance of a detection in the next fifty years.

And we're still ignoring the thickness of the galaxy, which is five thousand light years — call it about thirty-three domains deep — even out here.  So if we pretend the galaxy is an even five thousand light years thick all the way across, then the odds are on the order of thirty times worse than we just calculated. And at that, I've been VERY generous in SETI's favor throughout.

So ... how's the odds on that SETI program looking, huh...?

[1]  We're not going to try to correct for what the habitable and non-habitable regions of the galaxy might be, because bluntly we don't know enough about the answer to make the effort any more than pure guesswork and handwaving.  We can reasonably assume that the area in the immediate vicinity — let's be generous and say a thousand light years or so — of the supermassive black hole we believe to lie at the heart of the galaxy is probably pretty hostile to life; but then, that central bulge is sixteen thousand light years thick.  And we have found life in some pretty damned hostile environments here on earth, from ocean-floor vents to the cores of nuclear reactors.

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